The present invention relates to pipe thread cutting mechanisms and, more particularly, to mechanisms for controlling the position of the thread cutting members or chasers throughout the thread cutting operation.
Thread cutting die heads including the die heads capable of generating a tapered thread are well known in the art. Typical examples of such die heads are shown in U.S. Pat. Nos. 2,054,028; 2,163,598 and 2,848,726.
Such die heads include chasers mounted on slides for radial movement in a die head. In the use of such die heads it is necessary to position the chasers in their closed position to exact size, to recede the chasers, i.e. move them radially outward as the threading progresses to provide a tapered thread and to move the chasers radially outward further to full open position at the conclusion of a threading operation.
In general, separate control mechanisms have been provided to effect the various functions of sizing, receding, opening and closing. Usually the control apparatus includes cams, slides, levers, control rings or latch rings which must be made to very close tolerances to assure required accuracy. Such components are not only expensive to manufacture, but are subject to wear. Also adjustments in these mechanisms are complex, time consuming and require considerable expertise.
It is, accordingly, the principal purpose and object of the present invention to provide improved combined means for controlling all operative positions of the chasers including initial sizing, receding and opening and closing movements which eliminate the cost and complexity of prior systems.
It is a further object of the present invention to provide improved control means which are subject to reduced wear and thus have an extended service life.
It is also an object of the present invention to provide improved chaser position control means in which adjustments for size or other functions may be made quickly, easily and with precision.
Another object of the invention is to provide a thread cutting machine which is capable of accurate adjustment over a wide range of pipe sizes.
In accordance with another aspect of the present invention, pre-turning and threading of the pipe are accomplished by either of two rotary, receding-chaser die heads, depending on the pipe size being processed. A pre-calibrated, vernier-like system of cooperating keyways provides means for rapidly and accurately repositioning or replacing the holders at definite locations appropriate for each size of pipe being processed. These keyways are located in the back surfaces of the chaser holders and also in the mating faces of dovetailed die head slides to which the holders are attached. All chaser holders carry two tangential type chasers, with each chaser being arranged with independent adjustment and clamping means to permit optimum chaser positioning for each different set of operating circumstances.
The operating motions of the die head slides upon which the chaser holders are mounted originate at the rear of the headstock and are relayed forward to the die head by three parallel rods contained within the bore of the headstock spindle. These rods are connected by a common externally grooved ring which is positioned concentrically and rotates with the spindle and the die head. The grooved ring is engaged with a Y-shaped bell crank which operates as the taper control yoke, the rear portion of which contains an antifriction roller which runs on a sloped bar-type taper control cam.
As the headstock moves forward under the influence of the leadscrew in accordance with conventional practice during the threading operation, the roller in the trailing arm of the taper control yoke gradually descends the forwardly sloped cam, causing the rotating grooved ring with attached rods to move horizontally forward at a rate slightly faster than that of the headstock. This action is relayed by the rods to the head operating ring which, in turn, causes the dovetailed slides with their attached chaser holders to progressively recede at the proper rate. Opening and closing of the die head are accomplished through the same basic mechanism as that employed to recede the chasers, with means for rapid displacement of the taper control yoke.
Apparatus is also provided for positively limiting the closing motion of the die head in either single-cut mode or double-cut, i.e., roughing and finishing mode, through appropriate operation of the same mechanism employed to relay receding, opening and closing motions from their origins to the chaser holders.